ppc64le: Fix container registry setup task
ppc64le: Fix container registry setup task

The task fails with below error:-
Key 'registries.block.registries' has already
been defined in /etc/containers/registries.conf.

The key which contains 'registry.centos.org'
is 'unqualified-search-registries', let's use that
and it avoids duplicate declaration.

Change-Id: Ibcce8a1ae92af91540c22700b283f200658d6f7d

redhat-openstack/rdo-infra,rdo-infra/ci-config,rdo-infra/ci-config,redhat-openstack/rdo-infra,rdo-infra/ci-config,rdo-infra/ci-config,redhat-openstack/rdo-infra,redhat-openstack/rdo-infra